Fuel cell is typically composed of a plurality of single cells with each comprising two electrodes (bipolar plates) which are divided apart by an electrolyte element and assembled with each other in series to form a fuel cell stack. Electrochemical reaction is implemented by supplying proper reactants to each electrode, i.e., supplying fuel to one electrode and oxidant to the other electrode, as a result, potential difference is formed between the electrodes and accordingly, electric energy is generated.
To meet the demand of large-power output, increasing active area (catalyst layers) in membrane electrode assembly (MEA) of each cell is typically applied. As shown in FIG. 1, catalyst layers 2 are arranged at two sides (only the front side is shown in FIG. 1) of a proton exchange membrane 1 in FIG. 1, reactants entering channels of the bipolar plate from passages 4, and reactants released from the channels start electrochemical reaction on the catalyst layers 2 of the membrane electrode assembly (MEA).
In comparison with previous techniques, considerable improvements have been made in channel designs of the present bipolar plates although channels on the bipolar plate are still unable to guarantee the uniform conveyance of reactants during the process of electrochemical reaction, along with increase of active areas in the membrane electrode assembly (MEA). In the membrane electrode assembly (MEA), shown as FIG. 1, gas flow distribution is not uniform along channels of entire cell from entrance to exit, or in different local regions. In addition, for overall areas or local regions, concentration of fuel and oxidant are also uneven, and during working state, electrical transient effect generated by the fluctuation of reactants supply, and the relation between voltage V and length L from channel inlet to outlet are shown as FIG. 2. A fairly large voltage difference ΔV is possibly generated between two ends of the same channel with its length L; likewise, such a phenomenon of fairly large voltage difference could also be possibly generated in the transverse direction of the active areas of the membrane electrode assembly (MEA), and the generation of voltage difference caused by uneven delivery of reactants is also possible between the channels to generate a fairly large in-plane current inside each cell, as a result, electrochemical corrosion of membrane electrode is caused, and this will shorten the service life of fuel cell greatly. Further, performance of the regions with rich reactant supply is limited by the regions with poor reactant supply, such correlation effect will result in pulling down output voltage in the regions with rich reactant supply, so impact overall output power of the fuel cell.